A pure function is a function which
- Given the same input, always returns the same output.
- Produces no side effects.
- Pure functions must not mutate external state.
A function is only pure if, given the same input, it will always produce the same output.
Example :
PURE FUNCTION
function isValid(age){
return age >= 18;
}
This function will always return true or false based on age.
EXAMPLE OF UNPURE FUNCTION
- Pure functions must not mutate external state.
items = [];
const addItems = (item) => {
items.push({
item
});
};
addItems() is not a pure function because it mutates the external state by pushing values to that items array.
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